What kills a cone in a horn? - diyAudio
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Old 25th March 2013, 01:25 PM   #1
more10 is offline more10  Sweden
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Default What kills a cone in a horn?

Hornresp now shows pressure on the cone (instead of pressure at S1).

I am quite shure that the pressure by itself will not tear a cone. It must be a combination of pressure and the force that the current through the voice coil makes on the cone.

Is there a simple way to calculate the sheer force on the cone?

Mårten
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Old 25th March 2013, 02:40 PM   #2
AndrewT is offline AndrewT  Scotland
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Pressure and the acceleration times cone mass combined is what tears or collapses the cone.
Both are directly related to VC current.
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Old 25th March 2013, 04:48 PM   #3
jbell is offline jbell  United States
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stupidity behind the mixer kill cones in horns...

Stupid + Alcohol = 50% decline in cone strength.

That's about as close to a formula as I've got.
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Old 29th March 2013, 01:58 PM   #4
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Help your local reconer. Take RMS power rating x 4, turn bass to 10, turn mixer slider to 10..........,then add : I have been a DJ for 15 years:,,,,,cone blow out. All things have a fail point. Please use a Crown 5000 on your Cerwin Vega folded horns at full blast. Send blown woofers to me for repair. Sorry it is just one of those days. VECTORDJ
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Old 29th March 2013, 02:42 PM   #5
JMFahey is offline JMFahey  Argentina
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Quote:
Originally Posted by more10 View Post
Hornresp now shows pressure on the cone (instead of pressure at S1).

I am quite shure that the pressure by itself will not tear a cone. It must be a combination of pressure and the force that the current through the voice coil makes on the cone.

Is there a simple way to calculate the sheer force on the cone?

Mårten
I make speakers and in the course of experiments or new product development *have* torn speaker cones.

In fact there is one *killer* sounding combination which I can't make any more because of guaranteed failure within a couple months.

After autopsy, rather than sheer pressure itself, I saw the following destructive mechanism:
Imagine a rectilinear cone pointing up, seen from one side.
When VC starts going "up", not all the cone goes up at the same instant, because:

a) cone is not rigid (none is).

b) the accelerating force is not applied over all the surface but only at the apex of the cone.
More properly at the "neck" that joins VC and cone.

c) the cone, besides being flexible, has mass, so "the center" starts moving up before "the edge".
Net result is that the cone flexes forward.
Now the applied voltage inverts, same happens but in the opposite direction.

Net result is that the cone is *vigorously* (and that's an understatement) flexed.

And not in an uniform way, since the center moves up and down at a different phase than the edge, and sound/movement takes a definite time to travel center to edge, there's a (literally) wave going back and forth.
Which depending on frequency has nodes and peaks at different distances from the VC.

If strong and sustained enough, this causes a weakening of the cone and eventual failure.
I'm not talking about sheer cone tearing but flexion caused fatigue.

In my experiments, it usually happens between 20% and 30% of the distance from "neck" to edge.
I have tried reinforcing the "danger area" by cutting a proper sized ring from other cone and gluing it there.
It works ... but it *kills* the sound

I guess that's why "big" efficient speakers tend to use large diameter VC (say, 100 mm) and curvilinear cones (JBL/EV/etc.)
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Old 29th March 2013, 04:25 PM   #6
tb46 is offline tb46  United States
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Hi Y'all,

This part of this thread: TH-18 Flat to 35hz! (Xoc1's design) especially Post #693, by Tom Danley may be of interest.

Here is a neat pamphlet by Harman/Infinity on their C.M.M.D. cones: http://www.harmanaudio.com/all_about_audio/Cmmd.pdf

John Sheerin posted an interesting reference here, Post #6: cone breakup

Otherwise, you should be able to carefully tune just about any resonant mechanical system into self-destruct mode, particularly loudspeakers. All it takes is dilligence. :-)



Regards,
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Old 29th March 2013, 07:17 PM   #7
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Quote:
Originally Posted by JMFahey View Post

I'm not talking about sheer cone tearing but flexion caused fatigue.

I guess that's why "big" efficient speakers tend to use large diameter VC (say, 100 mm) and curvilinear cones (JBL/EV/etc.)
I have found curvilinear cones to be more subject to flexing induced failure than conical cones.
Curvilinear designs extend the upper response of cones because they allow some flexing.
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Old 29th March 2013, 08:02 PM   #8
PASC is offline PASC  Brazil
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Hi!

Throat cone rate should be adequate with all kind of horns.

What about failure limits: thermal and mechanical.

Stay within limits wih good projects loudspeakers (good drivers) will be alive.

My thougths.

Regards,
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Old 29th March 2013, 08:06 PM   #9
wg_ski is offline wg_ski  United States
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Curvilinear designs extend the upper response because they don't go to complete $ when they do break up. They're on the light side to get that extended high end, and light cones die if you hit em too hard (as 4pyros has found out - the exact failure pattern that JMFahey described). Build one stout enough to withstand 1000 watts in a horn and it won't have good HF resonse, which defeats the purpose of the curvilinear cone. Good HF response isn't needed in a sub. You've just gotta use the right tool for the job.

Back when more than 200 watts was a dream you could put an EVM15B in a horn with an 8 foot path and get away with it. Don't try it with a modern amp unless you want to support your local reconer.
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Old 29th March 2013, 08:18 PM   #10
Hentai is offline Hentai  Japan
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As JMFahey said it takes a while for the force to reach the outer edge of the cone. Now correct me if i'm wrong but the edge of the cone is where air load has the most influence, granted that in a horn's throat that resistance becomes much higher combined with the effect described by JMFahey you can visualize what cause the distruction of cone.
A good cone loudspeaker for horn loading has high voicecoil diameter but smaller overall diameter, but it all depends on the horn design. Usually compression ratio for bass horns is small so not to create problems.
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